Medically Reviewed

Complete vs. Incomplete Proteins: A Beginner's Guide

Thinking about incorporating protein supplements into your diet? Here's what you need to know about complete and incomplete proteins to get started.

You might be skeptical about protein. Right now, protein powders are booming, and while you might think they’re just for people looking to build lean muscle or bulk up, protein does so much more, and is an indispensable part of a healthy, balanced diet.

Proteins are biochemical molecules that contain chains of amino acids. Protein can help repair and create tissue (including muscle), is used to make hormones and enzymes, and is a building block for everything from cartilage and bones to hair and nails. Because our bodies use protein in so many ways, getting enough through your diet not only helps to give your body what is needs, but is essential for overall health. But not all protein contains the same amino acids, which is why you might have heard about “complete” and “incomplete” proteins.

So what exactly is the difference?

Here’s the gist: overall there are twenty different kinds of amino acids, eleven of which our bodies can produce on their own. The other nine, called “essential amino acids,” we can only get through diet, supplementation, or a combination of the two.

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A complete protein is one that contains all nine of those amino acids that our bodies need: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. While doctors generally agree that the best way to get protein is through diet, protein is generally found through animal sources, such as fish, poultry, meat, dairy products and eggs. Though there are some vegan sources, such as quinoa, beans, certain nuts and whole grains, it can be difficult to get the same levels of protein through a plant-based diet as from those one that includes animal products.

An incomplete protein is one that does not contain all nine of those essential amino acids. Beans, specific nuts, and tofu are a couple examples of incomplete protein sources, so eating those foods alone for protein will not give you all of the amino acids your body needs. That said, the more varied your diet, the more likely it is that you’re getting all the nutrients you need, so it is possible for vegetarians and vegans who eat a variety of different foods to get enough protein.

Many vegetarians and vegans combine different protein sources together, rather than trying to find only complete proteins, since combining different incomplete protein sources together in a dish can help create a complete protein meal. You’ve probably had several of these combinations without realizing it, like peanut butter on bread, hummus and pita, brown rice and beans or chili and cornbread, to name a few. Just take it from the FDA:

“Grains are low in the amino acid lysine, while beans and nuts (legumes) are low in the amino acid methionine. When grains and legumes are eaten together (such as rice and beans or peanut butter on whole wheat bread), they form a complete protein.”

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So who does this impact?

Most of us get enough protein through our diets. If fish, poultry, and eggs are a part of your regular diet, then don’t sweat it! You’re most likely getting enough protein.

The same can be said for vegans who are conscious of protein intake, whether that means skillfully combining complementary proteins, or choosing to eat complete proteins regularly.

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If you aren’t eating a lot of complete protein sources, or decide you want to add a protein supplement to your diet, look for a powder that’s a complete protein.

Think of it this way: why would you choose to take only some of the things your body needs (like six or seven of the essential amino acids), when you could get all nine from a single source? While some people opt for incomplete proteins geared towards specific health goals (like collagen, for example, which is a popular protein used to support hair, skin and nail health), if your goal is overall health and well-being, then a complete protein is the best way to go. Whey and casein are both complete proteins, and are a great place to start.

Complete plant-based protein powders do exist, and are usually made up from many different plant-based protein sources combined together to create a complete, vegan protein supplement.

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